Transport Vehicle

The present invention relates to a transport vehicle such as a dump truck, and more particularly to a transport vehicle with a vessel that rises and falls by extension and contraction of a hoist cylinder.

A transport vehicle such as a dump truck is provided with a vessel that can rise and fall (tilt) on the vehicle body, and loads an object to be transported such as crushed stone and earth and sand on the vessel to perform transport work. The vessel is provided to the vehicle body such that the front side thereof can pivot in the vertical direction with the rear side thereof as a fulcrum. The vessel is pivoted upwardly by extending a hoist cylinder that is interposed between the vehicle body and the vessel and that can be extended and contracted. The transport vehicle is provided with a hydraulic system including a hydraulic fluid source that supplies hydraulic fluid to the hoist cylinder, and a control valve device that is disposed between the hydraulic fluid source and the hoist cylinder and controls supply and discharge of the hydraulic fluid to and from the hoist cylinder.

The control valve device that controls the extension and contraction of the hoist cylinder has four switching positions of a neutral position, a raising position, a lowering position, and a floating position. The neutral position is a position where the supply and discharge of the hydraulic fluid to and from the hoist cylinder is interrupted to stop the driving of the hoist cylinder. The raising position is a position where the hoist cylinder is extended by the supply and discharge of the hydraulic fluid to and from the hoist cylinder to pivot the vessel upwardly. The lowering position is a position where the hoist cylinder is contracted by the supply and discharge of the hydraulic fluid to and from the hoist cylinder to pivot the vessel downwardly. The floating position is a position where the hoist cylinder is contracted by discharging the hydraulic fluid from the hoist cylinder using the own weight of the vessel to permit the free fall of the vessel.

The control valve device for the hoist cylinder is selectively switched to any one of the above-described four switching positions according to an operation of an operation lever by an operator. The switching of the control valve device is of a hydraulic pilot type, and is performed by a pilot pressure output from a solenoid valve controlled according to the operation of the operation lever (see, for example, Patent Document 1).

Patent Document 1: WO 2018/051582

In a case where the control valve device for the hoist cylinder is configured to be driven by inputting the pilot pressure as in the technology described in Patent Document 1, if a failure in which a hydraulic fluid source of the pilot pressure (for example, a pilot pump) loses the function of delivering the hydraulic fluid due to some factor, or a failure in which a prime mover for rotationally driving the pilot pump (the hydraulic fluid source of the pilot pressure) stops occurs, the pilot pressure is lost.

In this case, from the viewpoint of safety or the like, the control valve device is switched to the neutral position. However, while a predetermined pilot pressure is not input thereafter, the vessel cannot be pivoted, and the vessel is maintained at the posture (position) at the time of the occurrence of the failure.

As means for controlling the posture of the vessel (hoist cylinder), the transport vehicle generally includes a manual switching valve arranged between the hydraulic fluid source and the hoist cylinder in addition to the control valve device described above. This manual switching valve enables the hoist cylinder to contract by discharging the hydraulic fluid from the hoist cylinder using the own weight of the vessel, and the free fall of the vessel is permitted. In a case where the above-described failure occurs when the vessel is in a rising state (inclined state), the vessel can be shifted from the inclined state to a falling state (seated state) by the own weight by manually operating the manual switching valve. Since the manual switching valve is arranged outside the operation room, it is necessary for the operator to move onto the vehicle body outside the operation room and operate the manual switching valve. However, since the transport vehicle with the vessel inclined is in an unstable posture, it is desirable for the operator to perform a switching operation of the control valve device in the operation room without moving to the outside of the operation room.

The present invention has been made to solve the above problems, and an object thereof is to provide a transport vehicle that enables an operator to perform a switching operation of a control valve device in an operation room even if an original pilot hydraulic fluid source used for driving the control valve device for a hoist cylinder loses the function thereof.

The present application includes a plurality of means for solving the above problems. An example thereof is a transport vehicle including: a hydraulic fluid source that supplies hydraulic fluid; a hoist cylinder that is extended and contracted by supply and discharge of the hydraulic fluid to allow a vessel to rise and fall; a hydraulic pilot type first control valve device that has a plurality of switching positions switched according to an operation of an operation device arranged in an operation room and controls a flow of the hydraulic fluid supplied from the hydraulic fluid source to the hoist cylinder and a flow of return fluid from the hoist cylinder to a hydraulic operating fluid tank; a pilot circuit that generates a pilot pressure for driving the first control valve device from a pilot hydraulic fluid source according to the operation of the operation device and inputs the pilot pressure to the first control valve device; a steering circuit including a steering cylinder that is extended and contracted by the hydraulic fluid supplied from the hydraulic fluid source to steer a steered wheel and an accumulator that stores a pressure of the hydraulic fluid supplied from the hydraulic fluid source and is capable of using the stored pressure as an emergency hydraulic fluid source for the steering cylinder, in which the transport vehicle includes: a connection line that connects the steering circuit and the pilot circuit to each other; a second control valve device that is provided on the connection line and is switched between an interruption position where supply of the hydraulic fluid from the accumulator to the pilot circuit is interrupted and a supply position where the supply of the hydraulic fluid from the accumulator to the pilot circuit is allowed; and a controller that controls the second control valve device based on a state of the pilot hydraulic fluid source.

According to the present invention, since the second control valve device is provided on the connection line for connecting the steering circuit and the pilot circuit to each other, even if the original pilot hydraulic fluid source of the pilot circuit loses the function thereof, the accumulator of the steering circuit can be temporarily used as the pilot hydraulic fluid source of the pilot circuit by switching the second control valve device to the supply position. Therefore, even if the original function of the pilot hydraulic fluid source used for driving the first control valve device for the hoist cylinder is lost, the operator can perform the switching operation of the first control valve device by using the operation device in the operation room.

Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

Hereinafter, embodiments of a transport vehicle of the present invention will be described by using the drawings. In the present embodiment, a dump truck will be described as an example of the transport vehicle. It should be noted that the forward and rearward and leftward and rightward directions described in the specification are directions viewed from an operator on board the transport vehicle.

1 FIG. 1 FIG. First, a configuration of a dump truck as a transport vehicle according to a first embodiment will be described by using.is a side view for depicting a dump truck as a transport vehicle according to a first embodiment of the present invention.

1 FIG. 1 1 2 3 4 2 3 5 4 In, a dump truckis a large-sized transport vehicle operating in a mine or the like, and transports a cargo (object to be transported) such as mined ores and earth and sand. The dump truckincludes front wheelsand rear wheelsthat are rotatably arranged on both left and right sides of the front and rear parts of the vehicle, a vehicle bodythat can be traveled by the front wheelsand the rear wheels, and a vesselthat is mounted on the vehicle bodyso as to be capable of rising and falling (tilting).

2 2 53 54 3 2 FIG. The front wheelsare, for example, steered wheels that are steered by the operator. The front wheelsas the steered wheels are configured to be steered by extension and contraction of left and right steering cylindersand(seeto be described later) to be described later. The rear wheelsare, for example, driven wheels that are rotatably driven by a travel drive device (not illustrated).

4 11 12 11 13 12 23 11 12 15 21 51 13 1 13 1 16 2 17 5 18 1 1 FIG. 2 FIG. 2 FIG. 2 FIG. 2 FIG. The vehicle bodyincludes a framethat is a support structure extending in the forward and rearward directions (the lateral direction in), a buildingarranged at a front portion of the frame, and a cabarranged on the building. Various kinds of apparatuses such as a hydraulic operating fluid tank(seeto be described later) are attached to the frame. The buildinghouses various devices such as a prime moverand hydraulic pumpsand(seeto be described later) to be described later. The cabis an operation room on which the operator rides to control the vehicle. Various kinds of control apparatuses for the operator to control the dump truckare arranged in the cab, such as a travelling pedal (not illustrated) for allowing the dump truckto travel, a steering wheel(seeto be described later) to be described later, for steering the front wheels(steered wheels), an operation device(seeto be described later) to be described later, for operating the rising and falling (posture) of the vessel, and a display deviceto be described later, for displaying to control the dump truck.

5 5 11 22 11 5 22 5 11 5 22 5 22 5 5 5 22 22 1 FIG. 1 FIG. The vesselis a container for loading a cargo (object to be transported) such as ores and earth and sand. The rear side of the vesselis rotatably attached to the rear end part of the framesuch that the front side thereof pivots in the vertical direction with the rear side thereof as a fulcrum. A pair of left and right hoist cylinders(only one is illustrated in) is interposed between the frameand the vessel. The hoist cylindersare hydraulic actuators that are extended and contracted by supply and discharge of hydraulic fluid. The vesselis configured to pivot with respect to the framebetween a transport posture in which the vesselbecomes a falling state (seated state) by contraction of the hoist cylindersand is capable of loading the object to be transported, and a releasing posture in which the vesselbecomes a rising state (tilted state) by extension of the hoist cylindersand the object to be transported can be released from the vessel. In, the vesselindicated by a solid line is in the transport posture, while the vesselindicated by a two-dot chain line is in the releasing posture. In addition, the hoist cylinderindicated by a solid line is in a contracted state, while the hoist cylinderindicated by a two-dot chain line is in an extended state.

2 FIG. 2 FIG. 1 FIG. Next, a configuration of a hydraulic system in the transport vehicle according to the first embodiment will be described by using.is a hydraulic circuit diagram for depicting a configuration of a hydraulic system provided in the transport vehicle according to the first embodiment depicted in.

1 20 5 2 20 21 51 22 21 52 53 54 51 23 22 53 54 The dump truckincludes a hydraulic systemfor allowing the vesselto rise and fall and steering the front wheels. The hydraulic systemincludes a first hydraulic pumpand a second hydraulic pumpas hydraulic fluid sources for supplying hydraulic fluid, the pair of hoist cylindersdriven by the hydraulic fluid supplied from the first hydraulic pump, a steering circuitincluding a pair of left and right steering cylindersanddriven by the hydraulic fluid supplied from the second hydraulic pump, and the hydraulic operating fluid tankfor storing return fluid discharged from the hoist cylindersand the steering cylindersand.

21 51 23 21 51 21 51 15 15 15 19 15 19 15 80 The first hydraulic pumpand the second hydraulic pumpsuck hydraulic operating fluid from the hydraulic operating fluid tankand deliver high-pressure hydraulic operating fluid (hydraulic fluid). The first hydraulic pumpand the second hydraulic pumpare, for example, variable displacement pumps and have a regulator (not illustrated) for adjusting the pump displacement. The first hydraulic pumpand the second hydraulic pumpare driven by, for example, the prime mover. The prime moveris, for example, an engine or an electric motor. The prime moveris provided with a speed sensorfor sensing the rotational speed of the prime mover. The speed sensoroutputs a sensed signal according to the sensed rotational speed of the prime moverto a controller.

22 5 22 22 22 22 22 22 5 22 22 22 22 5 22 1 FIG. 2 FIG. 1 FIG. 1 FIG. 1 FIG. a b a b b a The hoist cylindersare single-stage or multi-stage (a three-stage type inand) hydraulic cylinders for allowing the vessel(see) to rise and fall. The hoist cylindershave bottom-side fluid chambers (hereinafter, referred to as bottom chambers)and rod-side fluid chambers (hereinafter, referred to as rod chambers). The hoist cylindersare extended when the hydraulic fluid is supplied to the bottom chambersand the return fluid is discharged from the rod chambers. The vesselbecomes the releasing posture by the extension of the hoist cylinders(a two-dot chain line in). The hoist cylindersare contracted when the hydraulic fluid is supplied to the rod chambersand the return fluid is discharged from the bottom chambers. The vesselbecomes the transport posture by the contraction of the hoist cylinders(a solid line in).

22 21 23 30 30 21 22 22 23 30 21 24 23 25 30 22 22 22 26 26 a b a b. The pair of hoist cylindersis connected to the first hydraulic pumpand the hydraulic operating fluid tankvia a hoist control valve device. The hoist control valve devicecontrols the flow of the hydraulic fluid supplied from the first hydraulic pumpto the pair of hoist cylindersand controls the flow of the return fluid discharged from the pair of hoist cylindersto the hydraulic operating fluid tank. The hoist control valve deviceis connected to the first hydraulic pumpvia a first delivery lineand to the hydraulic operating fluid tankvia a first return line. In addition, the hoist control valve deviceis connected to the bottom chambersand the rod chambersof the hoist cylindersvia a pair of actuator linesand

30 17 5 13 5 22 22 22 5 22 22 5 22 5 5 The hoist control valve devicehas four switching positions including a holding position, a raising position, a lowering position, and a floating position, and is configured to be switched to any one of the four switching positions according to an operation of the operation devicefor the vesselin the cab. The holding position is a position where the posture of the vesselis held by interrupting the supply and discharge of the hydraulic fluid to and from the hoist cylinders. The raising position is a position where the hoist cylindersare extended by the supply and discharge of the hydraulic fluid to and from the hoist cylindersto pivot the vesselupwardly. The lowering position is a position where the hoist cylindersare contracted by the supply and discharge of the hydraulic fluid to and from the hoist cylindersto pivot the vesseldownwardly. The floating position is a position where the hoist cylindersare contracted by the own weight of the vesselto permit the vesselto fall by the own weight.

30 31 32 30 31 32 33 34 35 31 32 33 34 35 The hoist control valve deviceis, for example, a combination of a first control valveand a second control valve. Specifically, the hoist control valve devicehas a first control valve, a second control valve, a high-pressure hydraulic line, a low-pressure hydraulic line, and a bypass hydraulic line. The first control valveand the second control valveare connected in parallel to each other via the high-pressure hydraulic line, the low-pressure hydraulic line, and the bypass hydraulic line.

31 32 31 31 31 31 31 32 32 32 32 32 32 a b a b a b a b. The first control valveand the second control valveare configured with, for example, hydraulic pilot type directional control valves having six ports and three positions. The first control valvehas a pair of pressure-receiving sectionsandto which a pilot pressure is input, and is configured to be switched among three switching positions of a neutral position N, a raising position R, and a floating position F. The first control valve is switched from the neutral position N to the raising position R by the input of the pilot pressure to one pressure-receiving section, and is switched from the neutral position N to the floating position F by the input of the pilot pressure to the other pressure-receiving section. The second control valvehas a pair of pressure-receiving sectionsandto which the pilot pressure is input, and is configured to be switched among three switching positions of a neutral position N, a raising position R, and a lowering position L. The second control valveis switched from the neutral position N to the raising position R by the input of the pilot pressure to one pressure-receiving section, and is switched from the neutral position N to the lowering position L by the input of the pilot pressure to the other pressure-receiving section

33 21 24 34 23 25 31 32 35 33 34 31 32 21 23 The high-pressure hydraulic lineis connected to the first hydraulic pumpvia the first delivery line. The low-pressure hydraulic lineis connected to the hydraulic operating fluid tankvia the first return line. When the first control valveand the second control valveare at the neutral position N, the bypass hydraulic linebrings the high-pressure hydraulic lineand the low-pressure hydraulic lineinto a communication state. Accordingly, when the first control valveand the second control valveare at the neutral position N, the first hydraulic pumpbecomes an unloaded state, and the delivery pressure thereof is maintained in a low pressure state close to the pressure of the hydraulic operating fluid tank.

31 22 22 22 26 26 32 22 22 22 26 26 a b a b a b a b. The output side (actuator port side) of the first control valveis connected to the bottom chambersand the rod chambersof the hoist cylindersvia the pair of actuator linesand. The output side (actuator port side) of the second control valveis connected to the bottom chambersand the rod chambersof the hoist cylindersvia the pair of actuator linesand

34 26 26 36 36 31 36 23 34 22 22 26 36 23 34 22 22 26 36 36 22 22 22 22 22 a b a b a a a b b b a b a b a b. The low-pressure hydraulic lineand the pair of actuator linesandare connected to each other via make-up check valvesandin a state of bypassing the first control valve. The check valvepermits the flow of the hydraulic operating fluid of the hydraulic operating fluid tankfrom the low-pressure hydraulic lineto the bottom chambersof the hoist cylindersvia the actuator line, and blocks the flow in the reverse direction. The check valvepermits the flow of the hydraulic operating fluid of the hydraulic operating fluid tankfrom the low-pressure hydraulic lineto the rod chambersof the hoist cylindersvia the actuator line, and blocks the flow in the reverse direction. The check valvesandhave a function of replenishing the hydraulic operating fluid to the bottom chambersand the rod chambersof the hoist cylindersto prevent a negative pressure in the bottom chambersand the rod chambers

34 26 26 37 37 31 37 37 30 36 36 37 22 22 37 22 22 a b a b a b a b a a b a. In addition, the low-pressure hydraulic lineand the pair of actuator linesandare connected to each other via relief valvesandin a state of bypassing the first control valve. The relief valvesandprevent an overload of the hoist control valve deviceand are connected in parallel with the make-up check valvesand. The relief valveis configured to open when an overload in the contraction direction acts on the hoist cylinders, and has a function of releasing an excess pressure in the bottom chambers. The relief valveis configured to open when an overload in the extension direction acts on the hoist cylinders, and has a function of releasing the excess pressure of the rod chambers

34 26 26 38 38 32 38 23 34 22 22 26 38 23 34 22 22 26 38 38 22 22 22 22 22 a b a b a a a b b b a b a b a b. The low-pressure hydraulic lineand the pair of actuator linesandare connected to each other via make-up check valvesandin a state of bypassing the second control valve. The check valvepermits the flow of the hydraulic operating fluid of the hydraulic operating fluid tankfrom the low-pressure hydraulic lineto the bottom chambersof the hoist cylindersvia the actuator line, and blocks the flow in the reverse direction. The check valvepermits the flow of the hydraulic operating fluid of the hydraulic operating fluid tankfrom the low-pressure hydraulic lineto the rod chambersof the hoist cylindersvia the actuator line, and blocks the flow in the reverse direction. The check valvesandhave a function of replenishing the hydraulic operating fluid to the bottom chambersand the rod chambersof the hoist cylindersto prevent a negative pressure in the bottom chambersand the rod chambers

39 35 34 39 21 39 21 23 A relief valvecapable of changing a relief set pressure is disposed between the bypass hydraulic lineand the low-pressure hydraulic line. The relief valveis configured to open when the delivery pressure of the first hydraulic pumpreaches the set pressure. That is, the relief valveregulates the maximum delivery pressure of the first hydraulic pumpand has a function of releasing the excess pressure of the hydraulic circuit to the hydraulic operating fluid tank.

20 40 31 32 30 17 5 31 31 31 32 32 32 40 41 15 42 43 44 41 45 45 41 42 43 44 23 46 41 46 45 41 45 48 41 45 48 41 80 a b a b The hydraulic systemincludes a pilot circuitthat generates a pilot pressure for driving the pilot hydraulic type first control valveand second control valveconfiguring the hoist control valve devicefrom a pilot hydraulic fluid source according to an operation of the operation devicefor the vessel, and inputs the pilot pressure to the pressure-receiving sectionsandof the first control valveand the pressure-receiving sectionsandof the second control valve. The pilot circuithas a pilot pumpdriven by the prime mover, and three solenoid valves,, andconnected to the pilot pumpvia a pilot line. A portion in the pilot linebetween the pilot pumpand the solenoid valves,, andis connected to the hydraulic operating fluid tankvia a pilot relief valve. The pilot pumpis a pilot hydraulic fluid source, and is, for example, a fixed displacement pump. The pilot relief valvedefines the maximum delivery pressure (the maximum pressure of the pilot line) of the pilot pump. The pilot lineis provided with a pressure sensorfor sensing the delivery pressure of the pilot pump(the pressure of the pilot line). The pressure sensoroutputs a sensed signal according to the sensed delivery pressure of the pilot pumpto the controller.

42 43 44 30 31 32 17 5 30 42 43 44 41 80 The three solenoid valves,, andswitch between input of the pilot pressure to the hoist control valve device(the first control valveand the second control valve) and interruption of the input according to an operation of the operation devicefor the vessel, so that the hoist control valve deviceis switched to any one of the four switching positions (the holding position, the raising position, the lowering position, and the floating position). The respective solenoid valves,, andoutput the pilot pressure generated from the hydraulic pressure of the pilot pumpaccording to a control signal (excitation current) from the controller.

42 30 31 31 32 32 23 31 31 32 32 43 30 31 31 23 31 31 44 30 32 32 23 32 32 42 43 44 31 32 31 32 a a a a b b b b The solenoid valveis used for switching the hoist control valve deviceto the raising position. In a case where a standby control signal (OFF signal) is input, one pressure-receiving sectionof the first control valveand one pressure-receiving sectionof the second control valveare communicated with the hydraulic operating fluid tank. In a case where a driving control signal (ON signal) is input, the pilot pressure is output to one pressure-receiving sectionof the first control valveand one pressure-receiving sectionof the second control valve. The solenoid valveis used for switching the hoist control valve deviceto the floating position. In a case where a standby control signal (OFF signal) is input, the other pressure-receiving sectionof the first control valveis communicated with the hydraulic operating fluid tank. In a case where a driving control signal (ON signal) is input, the pilot pressure is output to the other pressure-receiving sectionof the first control valve. The solenoid valveis used for switching the hoist control valve deviceto the lowering position. In a case where a standby control signal (OFF signal) is input, the other pressure-receiving sectionof the second control valveis communicated with the hydraulic operating fluid tank. In a case where a driving control signal (ON signal) is input, the pilot pressure is output to the other pressure-receiving sectionof the second control valve. It should be noted that in a case where all of the three solenoid valves,, andinterrupt the input of the pilot pressure to the first control valveand the second control valve, the first control valveand the second control valveare at the neutral position N.

30 31 32 The holding position of the hoist control valve deviceis a position where the first control valveand the second control valveare at the neutral position N.

31 21 22 22 22 22 22 23 32 21 22 22 22 22 22 23 22 5 a b a b a b a b The first control valveat the neutral position N interrupts the connection between the first hydraulic pumpand the bottom chambersand the rod chambersof the hoist cylinders, and interrupts the connection between the bottom chambersand the rod chambersand the hydraulic operating fluid tank. Similarly, the second control valveat the neutral position N interrupts the connection between the first hydraulic pumpand the bottom chambersand the rod chambersof the hoist cylinders, and interrupts the connection between the bottom chambersand the rod chambersand the hydraulic operating fluid tank. Therefore, the hoist cylinderscannot be driven, and the posture of the vesselis maintained.

30 31 32 31 21 22 22 22 22 23 32 21 22 22 22 22 23 21 22 22 22 23 22 a b a b a b The raising position of the hoist control valve deviceis a position where the first control valveis at the raising position R and the second control valveis at the raising position R. The first control valveat the raising position R connects the first hydraulic pumpand the bottom chambersof the hoist cylindersto each other, and connects the rod chambersof the hoist cylindersand the hydraulic operating fluid tankto each other. The second control valveat the raising position R connects the first hydraulic pumpand the bottom chambersof the hoist cylindersto each other, and interrupts the connection between the rod chambersof the hoist cylindersand the hydraulic operating fluid tank. Therefore, the hydraulic fluid from the first hydraulic pumpis supplied to the bottom chambersof the hoist cylinders, the return fluid is discharged from the rod chambersto the hydraulic operating fluid tank, and the hoist cylindersare extended.

30 31 32 31 21 22 22 22 22 22 23 32 21 22 22 22 22 23 21 22 22 22 23 22 a b a b b a b a The lowering position of the hoist control valve deviceis a position where the first control valveis at the neutral position N and the second control valveis at the lowering position L. The first control valveat the neutral position N interrupts the connection between the first hydraulic pumpand the bottom chambersand the rod chambersof the hoist cylinders, and interrupts the connection between the bottom chambersand the rod chambersand the hydraulic operating fluid tank. The second control valveat the lowering position L connects the first hydraulic pumpand the rod chambersof the hoist cylindersto each other, and connects the bottom chambersof the hoist cylindersand the hydraulic operating fluid tankto each other. Therefore, the hydraulic fluid from the first hydraulic pumpis supplied to the rod chambersof the hoist cylinders, the return fluid is discharged from the bottom chambersto the hydraulic operating fluid tank, and the hoist cylindersare contracted.

30 31 32 31 21 23 22 22 23 22 22 21 31 22 22 23 32 21 22 22 22 22 22 23 22 22 23 5 23 22 22 36 38 22 a b b a b a b a b b b The floating position of the hoist control valve deviceis a position where the first control valveis at the floating position F and the second control valveis at the neutral position N. The first control valveat the floating position F connects the first hydraulic pumpand the hydraulic operating fluid tankto each other, and connects the bottom chambersof the hoist cylindersand the hydraulic operating fluid tankto each other. It should be noted that the connection between the rod chambersof the hoist cylindersand the first hydraulic pumpvia the first control valveat the floating position F is interrupted, and the connection between the rod chambersof the hoist cylindersand the hydraulic operating fluid tankis interrupted. The second control valveat the neutral position N interrupts the connection between the first hydraulic pumpand the bottom chambersand the rod chambersof the hoist cylinders, and interrupts the connection between the bottom chambersand the rod chambersand the hydraulic operating fluid tank. Therefore, the return fluid is discharged from the bottom chambersof the hoist cylindersto the hydraulic operating fluid tankby the own weight of the vessel, the hydraulic operating fluid is supplied from the hydraulic operating fluid tankto the rod chambersof the hoist cylindersvia the make-up check valvesand, and the hoist cylindersare contracted.

52 53 54 55 51 53 54 53 54 23 55 51 56 23 57 55 53 54 58 59 The steering circuitincludes the pair of left and right steering cylindersand, and a steering valvefor controlling the flow of the hydraulic fluid supplied from the second hydraulic pumpto the steering cylindersandand the flow of the return fluid discharged from the steering cylindersandto the hydraulic operating fluid tank. The steering valveis connected to the second hydraulic pumpvia a high-pressure lineand to the hydraulic operating fluid tankvia a low-pressure line. The steering valveis also connected to the steering cylindersandvia steering linesand.

53 54 51 2 53 54 53 54 53 54 53 53 54 54 58 53 53 54 54 59 a a b b a b b a The left and right steering cylindersandare hydraulic actuators that are extended and contracted by the hydraulic fluid supplied from the second hydraulic pump, and steer the left and right front wheels. The left and right steering cylindersandhave bottom-side fluid chambers (hereinafter, referred to as bottom chambers)andand rod-side fluid chambers (hereinafter, referred to as rod chambers)and, respectively. The bottom chamberof the steering cylinderon the left side and the rod chamberof the steering cylinderon the right side are connected to each other via the steering line. The rod chamberof the steering cylinderon the left side and the bottom chamberof the steering cylinderon the right side are connected to each other via the steering line.

55 55 53 54 53 54 51 53 54 53 54 23 55 51 53 54 55 16 55 53 54 55 16 a a a b b b a b b The steering valvehas a directional control sectionfor controlling the flow direction (the bottom chambersandor the rod chambersand) of the hydraulic fluid supplied from the second hydraulic pumpto the left and right steering cylindersandand the flow direction of the return fluid discharged from the left and right steering cylindersandto the hydraulic operating fluid tank, and a flow rate adjusting sectionfor adjusting the flow rate of the hydraulic fluid supplied from the second hydraulic pumpto the left and right steering cylindersand. The directional control sectionis configured to be switched from a neutral position N to left and right steering positions L and R according to the rotational operation of the steering wheel. The flow rate adjusting sectionis configured to adjust the flow rate of the hydraulic fluid (the hydraulic fluid supplied to left and right steering cylindersand) flowing through the flow rate adjusting sectionby the rotational operation of the steering wheel.

55 16 55 51 55 55 55 55 55 53 53 54 54 59 53 53 54 54 58 23 55 55 53 54 16 2 FIG. a b a b a a b a a b a In the steering valvedepicted in, for example, when the steering wheelis rotated counterclockwise, the directional control sectionis switched to the steering position L on the left side. In this case, the hydraulic fluid of the second hydraulic pumppasses through the flow rate adjusting sectionfrom the left side to the right side via the directional control sectionat the steering position L on the left side. At this time, the flow rate of the hydraulic fluid is adjusted by the flow rate adjusting section, and the hydraulic fluid is returned to the directional control section. The hydraulic fluid returned to the directional control sectionis supplied to the rod chamberof the steering cylinderon the left side and the bottom chamberof the steering cylinderon the right side via the steering line. On the other hand, the hydraulic fluid of the bottom chamberof the steering cylinderon the left side and the rod chamberof the steering cylinderon the right side is discharged from the steering lineto the hydraulic operating fluid tankvia the directional control sectionof the steering valve. Accordingly, the left steering cylinderis contracted, and the right steering cylinderis extended, so that the left steering operation is performed according to the rotational operation of the steering wheel.

16 55 51 55 55 55 55 55 53 53 54 54 58 53 53 54 54 59 23 55 55 53 54 16 a b a b a a a b b a a In addition, when the steering wheelis rotated clockwise, the directional control sectionis switched to the steering position R on the right side. In this case, the hydraulic fluid of the second hydraulic pumppasses through the flow rate adjusting sectionfrom the right side to the left side via the directional control sectionat the steering position R on the right side. At this time, the flow rate of the hydraulic fluid is adjusted by the flow rate adjusting section, and the hydraulic fluid is returned to the directional control section. The hydraulic fluid returned to the directional control sectionis supplied to the bottom chamberof the steering cylinderon the left side and the rod chamberof the steering cylinderon the right side via the steering line. On the other hand, the hydraulic fluid of the rod chamberof the steering cylinderon the left side and the bottom chamberof the steering cylinderon the right side is discharged from the steering lineto the hydraulic operating fluid tankvia the directional control sectionof the steering valve. Accordingly, the left steering cylinderis extended and the right steering cylinderis contracted, so that the right steering operation is performed according to the rotational operation of the steering wheel.

61 56 61 51 56 23 62 62 56 56 61 62 53 54 16 61 53 54 51 53 54 51 An accumulatoris connected to the high-pressure line. The accumulatorstores the pressure of the hydraulic fluid supplied from the second hydraulic pump. The high-pressure lineis connected to the hydraulic operating fluid tankvia the relief valve. The relief valvedefines the maximum pressure of the high-pressure line. Thus, the high-pressure lineis held at a predetermined pressure by the accumulatorand the relief valve. This allows the driving of the steering cylindersandaccording to an operation of the steering wheelto be secured. The accumulatoris further configured such that the stored pressure thereof is available as an emergency hydraulic fluid source for the steering cylindersandin a case where the hydraulic fluid of the second hydraulic pumpcannot be supplied to the steering cylindersanddue to a failure of the second hydraulic pumpor the like.

52 40 71 56 52 61 55 45 40 71 In the present embodiment, the steering circuitis connected to the pilot circuitvia a connection line. Specifically, the high-pressure lineof the steering circuit(a portion between the connection part with the accumulatorand the steering valve) is connected to the pilot lineof the pilot circuitvia the connection line.

72 71 72 52 40 52 40 72 61 52 40 41 40 41 A pilot pressure compensation control valveis provided on the connection line. The pilot pressure compensation control valveis configured to be switched between an interruption position where supply of the hydraulic fluid from the steering circuitto the pilot circuitis interrupted and a supply position where the supply of the hydraulic fluid from the steering circuitto the pilot circuitis allowed. The pilot pressure compensation control valveenables the accumulatoras a safety device of the steering circuitto be used as an emergency pilot hydraulic fluid source for the pilot circuitwhen the pilot pump, which is the original pilot hydraulic fluid source of the pilot circuit, loses the function thereof, that is, when the delivery pressure of the pilot pumpis lowered.

72 73 71 74 73 The pilot pressure compensation control valvehas, for example, a pilot hydraulic type selector valvedisposed on the connection lineand a solenoid valvecapable of switching between input of the pilot pressure to the selector valveand interruption of the input.

73 52 40 71 52 40 71 73 73 73 73 61 40 40 73 73 73 73 73 73 73 73 23 a a b c b c b b The selector valveis configured to be switched, for example, between an open position O where supply of the hydraulic fluid from the steering circuitto the pilot circuitis allowed and communication in the connection lineis established, and a closed position C where the supply of the hydraulic fluid from the steering circuitto the pilot circuitis interrupted and the connection lineis closed. The selector valvehas a restrictorat the open position O. The restrictorof the selector valvereduces the pressure of the high-pressure hydraulic fluid stored in the accumulatorand supplies it to the pilot circuitto protect the pilot circuit. The selector valvehas a pressure-receiving sectionon one side and a springon the other side. The selector valveis configured to be switched to the closed position C when the pilot pressure is input to the pressure-receiving section, and to be switched to the open position O by the springwhen the input of the pilot pressure to the pressure-receiving sectionis interrupted (the pressure-receiving sectionis communicated with the hydraulic operating fluid tank).

74 41 73 73 71 74 73 80 74 73 73 23 74 73 73 b b b The solenoid valveallows the hydraulic pressure from the pilot pumpto be input to the pressure-receiving sectionof the selector valveas the pilot pressure via the connection line. The solenoid valveswitches between input of the pilot pressure to the selector valveand interruption of the input, according to a control signal (excitation current) from the controller. In a case where a standby control signal (OFF signal) is input, the solenoid valvecauses the pressure-receiving sectionof the selector valveto be communicated with the hydraulic operating fluid tank. In a case where a driving control signal (ON signal) is input, the solenoid valveoutputs the pilot pressure to the pressure-receiving sectionof the selector valve.

20 30 17 5 17 17 17 30 17 17 80 a a The hydraulic systemis configured such that the hoist control valve deviceis driven according to an operation of the operation devicefor the vessel. The operation deviceis configured with, for example, an electric lever device and has an operation leverthat is manually tilted by the operator. The operation deviceis operable in any one of four operation positions of a holding position, a raising operation position, a floating operation position, and a lowering operation position corresponding to the respective switching positions of the hoist control valve device(the holding position, the raising position, the floating position, and the lowering position). The operation leveris normally arranged at the holding position. The operation deviceoutputs an operation signal according to the operation position to the controller.

80 72 41 41 15 41 45 72 80 72 80 17 17 80 42 43 44 17 30 80 81 82 81 30 82 81 80 The controllercan control the pilot pressure compensation control valvebased on the state of the pilot hydraulic fluid source. The state of the pilot hydraulic fluid source includes, for example, the flow rate of the pilot pump, the rotational speed of the pilot pump(or may be the rotational speed of the prime mover), the delivery pressure of the pilot pump, and the pressure of the pilot line. The control target of the pilot pressure compensation control valveby the controllerincludes the switching position of the pilot pressure compensation control valve. The controlleris electrically connected to the operation device, and an operation signal of the operation deviceis input thereto. The controllerdirectly controls the three solenoid valves,, andaccording to the operation position (operation signal) of the operation device, thereby indirectly controlling the switching position of the hydraulic pilot type hoist control valve device. The controlleris configured with a computer including, for example, a storage deviceincluding a RAM, a ROM, and the like, and a processorincluding a CPU, an MPU, and the like. The storage devicepreliminarily stores a program and various kinds of information necessary for controlling the switching position of the hoist control valve device. The processorreads the program and the various kinds of information from the storage deviceappropriately and executes processing in accordance with the program, thereby realizing various kinds of functions. It should be noted that the controllermay be configured with one computer or a plurality of computers.

17 17 80 42 43 44 42 42 31 31 32 32 31 32 22 5 a a a When the operation leverof the operation deviceis operated to the raising operation position, the controlleroutputs a control signal of an ON signal (excitation current) to the solenoid valveand outputs a control signal of an OFF signal to the solenoid valvesandother than the solenoid valve. This causes the pilot pressure from the solenoid valveto be input to one pressure-receiving sectionof the first control valveand one pressure-receiving sectionof the second control valve, and causes each of the first control valveand the second control valveto be switched to the raising position R. Accordingly, the hoist cylindersare extended to bring the vesselinto the releasing posture (tilted state).

17 80 44 42 43 44 44 32 32 32 31 22 5 a b When the operation leveris operated to the lowering operation position, the controlleroutputs a control signal of an ON signal (excitation current) to the solenoid valveand outputs a control signal of an OFF signal to the solenoid valvesandother than the solenoid valve. Accordingly, the pilot pressure from the solenoid valveis input to the other pressure-receiving sectionof the second control valveto switch the second control valveto the lowering position L, and the first control valveis maintained at the neutral position N. Accordingly, the hoist cylindersare contracted to bring the vesselinto the transport posture (falling state).

17 80 43 42 44 43 43 31 31 31 32 21 23 31 32 22 22 23 31 22 22 23 31 5 22 a b a a When the operation leveris operated to the floating operation position, the controlleroutputs a control signal of an ON signal (excitation current) to the solenoid valveand outputs a control signal of an OFF signal to the solenoid valvesandother than the solenoid valve. Accordingly, the pilot pressure from the solenoid valveis input to the other pressure-receiving sectionof the first control valveto switch the first control valveto the floating position F, and the second control valveis maintained at the neutral position N. Therefore, the hydraulic fluid from the first hydraulic pumpis returned to the hydraulic operating fluid tankvia the first control valveat the floating position F and the second control valveat the neutral position N. In this case, the bottom chambersof the hoist cylindersare in communication with the hydraulic operating fluid tankvia the first control valveat the floating position F. Thus, the hydraulic fluid in the bottom chambersof the hoist cylindersis discharged to the hydraulic operating fluid tankvia the first control valveat the floating position F by the own weight of the vessel, and the hoist cylindersare contracted.

17 80 42 43 44 31 32 21 23 31 32 31 32 22 22 22 22 a a b In a case where the operation leveris at the holding position (neutral position), the controlleroutputs a control signal of an OFF signal to each of the solenoid valves,, and. This causes the first control valveand the second control valveto be maintained at the neutral position N without input of the pilot pressure. Therefore, the hydraulic fluid from the first hydraulic pumpis returned to the hydraulic operating fluid tankvia the first control valveand the second control valveat the neutral position N. In addition, the first control valveand the second control valveat the neutral positions N prevent discharge from the bottom chambersand the rod chambersof the hoist cylindersto the hydraulic operating fluid tank. That is, the hoist cylinderscan't be extended or contracted.

22 30 42 44 80 15 41 40 31 32 30 42 44 31 32 30 17 17 22 5 5 1 5 a As described above, the extension/contraction operation of the hoist cylindersis performed by switching of the hoist control valve devicevia the control of each of the solenoid valvestoby the controller. However, in a case where a failure in which the prime moveror the pilot pumpunintentionally stops due to some factor occurs, supply of the hydraulic fluid to the pilot circuitstops. Accordingly, since it becomes impossible to input the pilot pressure to the first control valveand the second control valveof the hoist control valve devicefrom each of the solenoid valvesto, the first control valveand the second control valveare at the neutral position N (the hoist control valve deviceis at the holding position) even if the operation leverof the operation deviceis at any operation position. In this case, it becomes impossible to perform the extension/contraction operation of the hoist cylinders, and the vesselis held in the posture at the time when the above-described failure occurs. In a case where the above-described failure occurs when the vesselis in the releasing posture (rising state), the dump truckis in an unstable posture in which the center of gravity is relatively raised. Therefore, it is necessary to shift the vesselfrom the inclined state to the falling state.

80 18 72 5 15 41 80 19 48 19 48 81 18 72 80 18 72 15 19 41 48 Therefore, the controllerof the present embodiment controls the display deviceto display a warning display for warning of an abnormality and also performs the switching control of the pilot pressure compensation control valvein order to enable the posture of the vesselto be changed, when detecting the abnormality in the rotational speed of the prime moveror the abnormality in the delivery pressure of the pilot pump. The controlleris electrically connected to the speed sensorand the pressure sensor, and a sensed signal of the speed sensorand a sensed signal of the pressure sensorare input thereto. The storage devicepreliminarily stores a program and various kinds of information necessary for controlling the display deviceand the pilot pressure compensation control valve. The controllercontrols the display of the display deviceand controls the pilot pressure compensation control valvebased on the rotational speed (sensed signal) of the prime moversensed by the speed sensorand the delivery pressure (sensed signal) of the pilot pumpsensed by the pressure sensor.

72 2 FIG. 6 FIG. 3 FIG. 2 FIG. 4 FIG. 2 FIG. 5 FIG. 4 FIG. 6 FIG. 4 FIG. Next, an example of a control procedure of the pilot pressure compensation control valveby the controller of the transport vehicle according to the first embodiment will be described by usingto.is a flowchart for depicting an example of a control procedure of the pilot pressure compensation control valve in the controller of the hydraulic system of the transport vehicle according to the first embodiment depicted in.is a schematic diagram for depicting an example of the display device of the transport vehicle according to the first embodiment depicted in.is a diagram for depicting an example of a warning display displayed on the display device of the transport vehicle according to the first embodiment depicted in.is a diagram for depicting another example of a warning display displayed on the display device of the transport vehicle according to the first embodiment depicted in.

80 72 80 80 74 72 74 10 74 3 FIG. The controllerof the present embodiment starts a control flow of the pilot pressure compensation control valvedepicted inby turning on the power supply of the controller(Start). First, the controlleroutputs a control signal of an ON signal to the solenoid valveconfiguring the pilot pressure compensation control valveto excite the solenoid valve(Step S). This causes the solenoid valveto be switched to an output position where the pilot pressure can be output.

80 15 1 20 15 30 15 81 30 15 19 19 40 19 80 Next, the controllerstarts the prime moveraccording to an operation of a key cylinder (not illustrated) of the dump truck(Step S), and determines whether or not the rotational speed of the prime moveris within a normal range (Step S). The normal range of the rotational speed of the prime moveris preliminarily set and preliminarily stored in the storage device. Step Sis a step for determining the presence or absence of an abnormality when the prime moveris started. Specifically, it is determined whether or not the sensed value of the speed sensoris within a normal range. When the sensed value of the speed sensoris within the normal range (YES), the flow proceeds to Step S, and when the sensed value of the speed sensoris out of the normal range (NO), the flow proceeds to Step S.

15 30 80 15 80 15 When the rotational speed of the prime moveris out of the normal range (NO) in Step S, the controllernotifies an abnormality in the rotational speed of the prime mover(Step S). After notifying the abnormality in the prime mover, the control flow is terminated.

80 18 18 15 18 18 18 18 15 18 18 18 4 FIG. 5 FIG. a b c b c The controllercontrols the display devicesuch that, for example, the display devicedisplays a warning display for warning of the abnormality in the prime mover. For example, as depicted in, the display devicehas instruments, a message display section, a lamp lighting section, and the like. The warning display for warning of the abnormality in the prime moveris, for example, the warning display depicted in, and is displayed on the message display sectionof the display device. It should be noted that it is also possible to control the lamp lighting sectionso as to light a lamp.

30 15 80 15 40 15 41 81 40 15 41 41 40 19 19 50 19 70 On the other hand, when it is determined in Step Sthat the rotational speed of the prime moveris within the normal range (YES), the controllerdetermines whether the rotational speed of the prime moveris equal to or larger than a speed threshold value (Step S). The speed threshold value is a predetermined value based on such a rotational speed of the prime moverthat the delivery pressure of the pilot pumpis equal to or larger than a pressure threshold value to be described later, and is preliminarily stored in the storage device. That is, Step Sis a step for determining whether the rotational speed of the prime moverfor driving the pilot pumphas reached the rotational speed at which the pilot pumpcan supply a pressure required for the pilot circuit. Specifically, it is determined whether the sensed value of the speed sensoris equal to or larger than the speed threshold value. When the sensed value of the speed sensoris equal to or larger than the speed threshold value (YES), the flow proceeds to Step S, and when the sensed value of the speed sensoris smaller than the speed threshold value (NO), the flow proceeds to Step S.

40 15 80 41 50 40 31 32 30 81 48 48 60 48 30 When it is determined in Step Sthat the rotational speed of the prime moveris equal to or larger than the speed threshold value (YES), the controllerdetermines whether the delivery pressure of the pilot pumpis smaller than the pressure threshold value (Step S). The pressure threshold value is a predetermined value based on the minimum pressure required for the pilot circuit(pressure that secures a pilot pressure at which switching control of the first control valveand the second control valveof the hoist control valve deviceis possible), and is preliminarily stored in the storage device. Specifically, it is determined whether the sensed value of the pressure sensoris smaller than the pressure threshold value. When the sensed value of the pressure sensoris smaller than the pressure threshold value (YES), the flow proceeds to Step S, and when the sensed value of the pressure sensoris equal to or larger than the pressure threshold value (NO), the flow returns to Step S.

50 41 15 41 15 41 30 50 41 40 73 73 71 74 72 73 72 52 40 2 FIG. b When it is determined in Step Sthat the delivery pressure of the pilot pumpis equal to or larger than the pressure threshold value (NO), the prime moverand the pilot pumpare normally functioning. When the functions of the prime moverand the pilot pumpare normally maintained, the processing of Steps Sto $is repeated. At this time, the pressure from the pilot pump(pilot circuit) depicted inis input as the pilot pressure to the pressure-receiving sectionof the selector valvevia the connection lineand via the solenoid valvein the excited state (output position) of the pilot pressure compensation control valve, and the selector valveis in a state of being switched to the closed position C. That is, the pilot pressure compensation control valveis at the interruption position, and the connection between the steering circuitand the pilot circuitis interrupted.

50 41 80 41 40 60 80 18 41 41 18 18 18 6 FIG. 4 FIG. b c On the other hand, when it is determined in Step Sthat the delivery pressure of the pilot pumpis smaller than the pressure threshold value (YES), the controllernotifies an abnormality in the pressure of the pilot pump(pilot circuit) (Step S). For example, the controllercontrols the display deviceso as to display a warning display for warning of the abnormality in the pressure of the pilot pump. The warning display for warning of the abnormality in the pressure of the pilot pumpis, for example, the warning display depicted in, and is displayed on the message display sectionof the display devicedepicted in. It should be noted that it is also possible to control the lamp lighting sectionso as to light a lamp.

60 40 15 80 72 70 80 74 72 74 74 73 73 23 41 73 73 71 74 73 b b After execution of the processing of Step Sor when it is determined in Step Sthat the rotational speed of the prime moveris smaller than the speed threshold value (NO), the controllerswitches the pilot pressure compensation control valveto the supply position (Step S). Specifically, the controlleroutputs a control signal of an OFF signal to the solenoid valveof the pilot pressure compensation control valve(the output of the excitation current is stopped), and sets the solenoid valveto a non-excitation state. Accordingly, since the solenoid valveis switched to a position where the pressure-receiving sectionof the selector valveis connected to the hydraulic operating fluid tank, the input of the pilot pressure from the pilot pumpto the pressure-receiving sectionof the selector valvevia the connection lineis interrupted by the solenoid valve. As a result, the selector valveis switched to the open position O.

15 41 30 50 15 40 41 50 31 32 30 31 32 5 1 For example, when the prime moverand the pilot pumpare in a normal state and the processing of Steps Sto Sis being repeated, if an abnormality occurs in the prime mover(NO in Step S) or an abnormality occurs in the pilot pump(YES in Step S), the pilot pressure for driving the first control valveand the second control valveof the hoist control valve devicecannot be secured. This is a situation where the original function of the pilot hydraulic fluid source for the first control valveand the second control valveis lost. In a case where the loss of the function of the pilot hydraulic fluid source occurs when the vesselis in a rising state (releasing posture), the dump truckbecomes an unstable posture.

80 72 73 70 61 52 73 73 40 31 32 30 61 52 72 73 17 5 13 43 40 31 31 30 61 a b At this time, if the controllerswitches the pilot pressure compensation control valveto the supply position (the selector valveto the open position O) in Step S, the pressure stored in the accumulatorof the steering circuitcan be reduced by the restrictorof the selector valveand be supplied to the pilot circuit. That is, even where the original function of the pilot hydraulic fluid source is lost for the first control valveand the second control valveof the hoist control valve device, the accumulatorof the steering circuitcan be used as the emergency pilot hydraulic fluid source by the switching control of the pilot pressure compensation control valve(selector valve). Therefore, if the operator switches the operation devicefor the vesselin the cabto the floating operation position, the pilot pressure can be input from the solenoid valveof the pilot circuitto the other pressure-receiving sectionof the first control valveof the hoist control valve deviceby using the accumulatoras the pilot hydraulic fluid source.

31 22 22 23 31 5 22 5 a Accordingly, since the first control valveis switched to the floating position F, the return fluid is discharged from the bottom chambersof the hoist cylindersin the extended state to the hydraulic operating fluid tankvia the first control valveat the floating position F by the own weight of the vessel. As a result, the hoist cylindersin the extended state are contracted, and the vesselis changed to the falling transport posture.

72 73 61 52 40 30 17 13 13 As described above, by switching the pilot pressure compensation control valveto the supply position (the selector valveto the open position O) in the present embodiment, the accumulatorof the steering circuitis used as the emergency pilot hydraulic fluid source for the pilot circuit. Accordingly, the operator can perform the switching control of the hoist control valve deviceby operating the operation devicein the cabwithout moving outside the cab.

1 21 51 22 5 30 17 13 21 22 22 23 40 30 41 17 52 53 54 51 2 61 51 53 54 1 71 52 40 72 71 72 61 52 40 61 40 As described above, the dump truck(transport vehicle) according to the first embodiment includes the first hydraulic pumpand the second hydraulic pumpas hydraulic fluid sources for supplying hydraulic fluid, the hoist cylindersthat are extended and contracted by supply and discharge of the hydraulic fluid to allow the vesselto rise and fall, the hydraulic pilot type hoist control valve device(first control valve device) that has a plurality of switching positions switched according to an operation of the operation devicearranged in the operation roomand controls the flow of the hydraulic fluid supplied from the first hydraulic pump(hydraulic fluid source) to the hoist cylindersand the flow of the return fluid from the hoist cylindersto the hydraulic operating fluid tank, the pilot circuitthat generates the pilot pressure for driving the hoist control valve device(first control valve device) from the pilot pumpas the pilot hydraulic fluid source according to the operation of the operation deviceand inputs the pilot pressure to the hoist control valve device (first control valve device), and the steering circuitincluding the steering cylindersandthat are extended and contracted by the hydraulic fluid supplied from the second hydraulic pump(hydraulic fluid source) to steer the front wheels(steered wheels) and the accumulatorthat stores the pressure of the hydraulic fluid supplied from the second hydraulic pump(hydraulic fluid source) and is capable of using the stored pressure as the emergency hydraulic fluid source for the steering cylindersand. The dump truck(transport vehicle) includes the connection linefor connecting the steering circuitand the pilot circuitto each other, and the pilot pressure compensation control valve(second control valve device) provided on the connection line. The pilot pressure compensation control valve(second control valve device) is configured to be switched between the interruption position C where supply of the hydraulic fluid from the accumulatorof the steering circuitto the pilot circuitis interrupted and the supply position O where the supply of the hydraulic fluid from the accumulatorto the pilot circuitis allowed.

72 71 52 40 41 40 61 52 40 72 41 30 30 17 13 According to this configuration, since the pilot pressure compensation control valve(second control valve device) is provided on the connection linefor connecting the steering circuitand the pilot circuitto each other, even if the pilot pumpthat is the original pilot hydraulic fluid source of the pilot circuitloses the function thereof, the accumulatorof the steering circuitcan be temporarily used as the pilot hydraulic fluid source of the pilot circuitby switching the pilot pressure compensation control valve(second control valve device) to the supply position. Therefore, even if the function of the pilot pumpthat is the original pilot hydraulic fluid source used for driving the hoist control valve device(first control valve device) is lost, the operator can perform the switching operation of the hoist control valve device(first control valve device) by the operation devicein the operation room.

72 71 73 71 71 74 73 In addition, in the present embodiment, the pilot pressure compensation control valve(second control valve device) is provided on the connection line, and has the pilot hydraulic type selector valvethat is switched between the closed position C where the connection lineis closed and the open position O where communication of the connection lineis established, and the solenoid valvecapable of switching between input of the pilot pressure to the selector valveand interruption of the input.

74 73 74 According to this configuration, since the solenoid valveis a valve that outputs the pilot pressure for driving the selector valve, the excitation current of the solenoid valvecan be lowered and the power consumption can be reduced as compared with a solenoid valve used for a main hydraulic circuit. Further, the size of the valve can be reduced.

72 73 a In addition, in the present embodiment, the pilot pressure compensation control valve(second control valve device) has the restrictorat the supply position.

61 52 40 72 61 73 40 a According to this configuration, when a pressure is supplied from the accumulatorof the steering circuitto the pilot circuitvia the pilot pressure compensation control valve, the high pressure of the accumulatoris reduced by the restrictor, and thus the pilot circuitcan be protected.

1 48 41 80 72 80 72 48 72 48 In addition, the dump truck(transport vehicle) according to the present embodiment includes the pressure sensorfor sensing the pressure of the pilot pump(pilot hydraulic fluid source) and the controllerfor controlling the pilot pressure compensation control valve(second control valve device). The controllercontrols the pilot pressure compensation control valve(second control valve device) to the interruption position C when the sensed value of the pressure sensoris equal to or larger than the preset pressure threshold value, and controls the pilot pressure compensation control valve(second control valve device) to the supply position O when the sensed value of the pressure sensoris smaller than the pressure threshold value.

41 48 72 5 17 41 According to this configuration, when an abnormality in the pilot pump(pilot hydraulic fluid source) is detected on the basis of the sensed value of the pressure sensor, the pilot pressure compensation control valve(second control valve device) is switched from the interruption position C to the supply position O without an operation by the operator, and thus the operator can change the posture of the vesselonly by operating the operation devicewhen the abnormality occurs in the pilot pump(pilot hydraulic fluid source).

41 15 1 19 15 80 72 80 72 19 In addition, in the present embodiment, the pilot hydraulic fluid source is the pilot pumpdriven by the prime mover. The dump truck(transport vehicle) includes the speed sensorfor sensing the rotational speed of the prime moverand the controllerfor controlling the pilot pressure compensation control valve(second control valve device). The controlleris configured to control the pilot pressure compensation control valve(second control valve device) to the supply position O in a case where the sensed value of the speed sensoris smaller than the preset speed threshold value.

15 19 72 5 17 41 15 According to this configuration, when an abnormality in the prime moveris detected on the basis of the sensed value of the speed sensor, the pilot pressure compensation control valve(second control valve device) is switched to the supply position O without an operation by the operator, and thus the operator can change the posture of the vesselonly by operating the operation devicewhen a normal pilot pressure cannot be generated from the pilot pumpdue to the abnormality in the prime mover.

80 72 19 48 In addition, in the present embodiment, the controlleris configured to control the pilot pressure compensation control valve(second control valve device) to the interruption position C when the sensed value of the speed sensoris equal to or larger than the speed threshold value and when the sensed value of the pressure sensoris equal to or larger than the pressure threshold value.

15 41 52 40 72 52 40 According to this configuration, when the prime moverand the pilot pumpare normally operated, the connection between the steering circuitand the pilot circuitis interrupted by the pilot pressure compensation control valve(second control valve device). This allows the steering circuitand the pilot circuitto be prevented from exerting influence on each other.

7 FIG. 7 FIG. 7 FIG. 1 FIG. 6 FIG. Next, a transport vehicle according to a second embodiment of the present invention will be described by using.is a hydraulic circuit diagram for depicting a configuration of a hydraulic system provided in the transport vehicle according to the second embodiment. It should be noted that in, parts having the same reference numerals as those depicted intoare similar parts, and thus the detailed description thereof will be omitted.

72 20 20 20 2 FIG. The transport vehicle according to the second embodiment differs from the first embodiment in that configurations of a pilot pressure compensation control valveA of a hydraulic systemA is different. Other configurations of the hydraulic systemA of the transport vehicle according to the second embodiment are similar to those of the hydraulic system(see) of the first embodiment, and thus the description thereof will be omitted.

72 71 72 52 40 71 52 40 71 72 61 52 40 41 40 Specifically, the pilot pressure compensation control valveA is configured with only one solenoid selector valve provided on the connection line, and does not include any other valve mechanisms. The solenoid selector valveA is configured to be switched between a supply position where supply of the hydraulic fluid from the steering circuitto the pilot circuitis allowed, that is, an open position O where communication of the connection lineis established, and an interruption position where the supply of the hydraulic fluid from the steering circuitto the pilot circuitis interrupted, that is, a closed position C where the connection lineis closed. As similar to the first embodiment, the pilot pressure compensation control valveA also enables the accumulatorof the steering circuitto be used as the emergency pilot hydraulic fluid source for the pilot circuitwhen the pilot pumpthat is the original pilot hydraulic fluid source of the pilot circuitloses the function thereof.

72 73 0 73 72 61 40 72 73 72 80 72 72 80 a a c The solenoid selector valveA has a restrictorat the open position(supply position). As similar to the first embodiment, the restrictorof the solenoid selector valveA reduces the pressure of the high-pressure hydraulic fluid stored in the accumulatorand supplies it to the pilot circuit. The solenoid selector valveA has a springon one side. The solenoid selector valveA is switched between the open position O and the closed position C according to a control signal (excitation current) from the controller. The solenoid selector valveA is, for example, a normally-open solenoid valve. That is, the solenoid selector valveA is configured to be switched to the open position O when a standby control signal (OFF signal) is input from the controller, and to be switched to the closed position C when a driving control signal (ON signal) is input.

80 72 72 80 72 80 10 15 40 41 50 72 80 70 31 32 30 61 52 40 72 3 FIG. 3 FIG. 3 FIG. 3 FIG. 3 FIG. It should be noted that the switching control of the controllerfor the pilot pressure compensation control valveA of the present embodiment is similar to the switching control for the pilot pressure compensation control valveof the first embodiment. That is, when the control flow (see) by the controlleris started, the solenoid selector valve (pilot pressure compensation control valve)A is switched to the closed position C (interruption position) by an ON signal from the controller(Step Sdepicted in). In addition, in a case where an abnormality occurs in the prime mover(in the case of NO in Step Sdepicted in) or in a case where an abnormality occurs in the pilot pump(in the case of YES in Step Sdepicted in), the solenoid selector valve (pilot pressure compensation control valve)A is switched to the open position O (supply position) by an OFF signal from the controller(Step Sdepicted in). Thus, even in the present embodiment, as similar to the first embodiment, even where the original function of the pilot hydraulic fluid source is lost for the first control valveand the second control valveof the hoist control valve device, the accumulatorof the steering circuitcan be used as the emergency pilot hydraulic fluid source for the pilot circuitby switching the pilot pressure compensation control valveA to the supply position (open position O).

72 71 52 40 41 40 61 52 40 72 41 30 30 17 13 According to the transport vehicle of the above-described second embodiment, since the pilot pressure compensation control valveA (second control valve device) is provided on the connection linefor connecting the steering circuitand the pilot circuitto each other as similar to the above-described first embodiment, even if the pilot pumpthat is the original pilot hydraulic fluid source of the pilot circuitloses the function thereof, the accumulatorof the steering circuitcan be temporarily used as the pilot hydraulic fluid source of the pilot circuitby switching the pilot pressure compensation control valveA (second control valve device) to the supply position O. Therefore, even if the function of the pilot pumpthat is the original pilot hydraulic fluid source used for driving the hoist control valve device(first control valve device) is lost, the operator can perform the switching operation of the hoist control valve device(first control valve device) by the operation devicein the operation room.

72 20 71 71 71 In addition, in the present embodiment, the pilot pressure compensation control valveA (second control valve device) of the hydraulic systemA is provided on the connection line, and has the solenoid type selector valve that is switched between the closed position C where the connection lineis closed and the open position O where communication of the connection lineis established.

72 72 According to this configuration, since the pilot pressure compensation control valveA (second control valve device) is configured with one valve mechanism, the number of parts of the pilot pressure compensation control valveA can be reduced as compared with the first embodiment.

It should be noted that the present invention is not limited to the first and second embodiments described above, but includes various modified examples. The above-described embodiments have been described in detail for the purpose of clearly explaining the present invention, and are not necessarily limited to those having all the described configurations. For example, a part of a configuration of an embodiment can be replaced with a configuration of another embodiment, or a configuration of an embodiment can be added to a configuration of another embodiment. In addition, a part of a configuration of each embodiment can be added to, deleted from, or replaced with another configuration.

30 31 32 For example, in the first and second embodiments described above, an example of a configuration in which the hoist control valve deviceincludes two control valves of the first control valveand the second control valveis depicted. However, the hoist control valve device can be configured with a single directional control valve. In this case, the hoist control valve device can be configured with, for example, a hydraulic pilot type control valve having six ports and four positions. This single control valve may be configured to have four switching positions of a neutral position as a holding position, a raising position, a lowing position, and a floating position.

1 : dump truck (transport vehicle) 2 : front wheel (steered wheel) 5 : vessel 13 : cab (operation room) 17 : operation device 19 : speed sensor 21 : first hydraulic pump (hydraulic fluid source) 22 : hoist cylinder 23 : hydraulic operating fluid tank 30 : hoist control valve device (first control valve device) 40 : pilot circuit 41 : pilot pump (pilot hydraulic fluid source) 48 : pressure sensor 51 : second hydraulic pump (hydraulic fluid source) 52 : steering circuit 53 54 ,: steering cylinder 61 : accumulator 71 : connection line 72 : pilot pressure compensation control valve (second control valve device) 73 : selector valve 73 a : restrictor 74 : solenoid valve 72 A: pilot pressure compensation control valve (second control valve device, solenoid type selector valve) 80 : controller